Joint prostheses

ABSTRACT

A component ( 1 ) of a prosthetic joint comprising a portion to secure the component to a bone and a bearing portion having a bearing surface ( 3 ) wherein one more reservoir ( 6 ) are situated behind the bearing surface ( 3 ), one or more magnet assemblies ( 5 ) are associated with the or each reservoir ( 6 ) and one or more passages ( 7 ) are provided extending between a surface of the component and the or each reservoir ( 6 ), and wherein either the bearing surface ( 3 ) includes magnetic material or a material that in use has a magnetic surface or the component ( 1 ) is adapted for use with a further joint component ( 2 ) which has a bearing surface ( 4 ) that includes magnetic material or a material that in use has a magnetic surface.

The present invention relates to replacement joints (joint prostheses)and in particular to improvements to the longevity of such joints.

Total replacement of joints, such as hip joints, is considered as animmensely successful procedure. Despite this, the major limiting factorregarding the longevity of this type of surgery is the process ofosteolysis (bone resorption) and aseptic loosening which ultimatelyleads to implant failure and the need for revision surgery. Thisphenomenon is attributed by most researchers in the field as beingdirectly related to the production of wear particles from the bearingsurface, resulting in wear debris thought to play a role in a form ofimmune cell reaction at the prosthesis/bone interface, causing boneresorption and implant loosening. The revision surgery needed as aresult of loosening incurs a high degree of morbidity for the patientand can be complex and costly. Accordingly, the goal of many researchefforts over the past 30 years in this field has been directed towardsprevention of these problems.

Published research has suggested that by minimising wear debrisproduction, the resulting bone resorption is minimised or evenprevented. This philosophy has resulted in the widespread clinical useof bearing designs that avoid ultra high molecular weight polyethylene(UHMWPE), the main cause of wear related debris in currently implantedprostheses. Typical examples of new bearing designs in routine clinicaluse include high hardness metal-on-metal and ceramic-on-ceramicbearings. Animal and clinical investigations have also examined surfacemodified coatings such as titanium nitride and diamond-like carbon.Despite much research, however, no bearing surface has been shown to beideal.

Metal-on-metal bearings are typically manufactured fromcobalt-chromium-molybdenum alloy (CoCrMo; e.g. ASTM F75-98, F799-99 orF1537-00). This bearing surface produces 20-100 times less volumetricwear (1-2 mm³/year) than the standard metal or ceramic on UHMWPE.Despite this reduction in volumetric wear, the particles produced bymetal-on-metal bearings are much smaller in size (down to 10 nm) thanUHMWPE particles resulting in larger numbers per unit volume. This isimportant as the large numbers of small particles produced has thepotential for exacerbating the inflammatory response rather thanreducing it. Further, reports of significantly raised serum cobalt andchromium levels in patients having received these implants has raisedconcern about their safety. These ions have been linked with systemicdisease including chromosomal damage and cancer.

Ceramic-on-ceramic bearings, mainly produced from alumina or zirconia invarious combinations, can also provide a low wear bearing surface withvolumetric wear rates similar to or slightly better than that ofmetal-on-metal. There are, however, several major drawbacks to ceramicimplants. Their hardness and brittleness makes them difficult andexpensive to manufacture as well as predisposing them to fracture afterimplantation. This fragility also requires the surgeon to insert theprosthesis with a very exacting technique making the surgery moredemanding.

Surface engineering techniques, such as thin surface coatings oftitanium nitride and diamond-like carbon have yet to be proven useful.Initial simulator and implant tests revealed their weakness todelamination from the underlying substrate and subsequent failure.

With the above in mind, some have acknowledged that the production ofwear debris cannot be prevented, only minimised. These researchers havedeveloped methods to prevent wear debris from reaching theprosthesis/bone interface where the end-result of bone resorption iseffected. A number of inventions have included ‘encapsulating’ hiparthroplasties where the bearing is surrounded by a semi- ornon-permeable membrane that traps debris. Others have attempted toattach semi-permeable (e.g. Gore-Tex) membranes around the superficialjoint interfaces of the prosthesis and bone in order to prevent weardebris accessing the deeper interfaces. These devices have not met withany degree of acceptance as they are cumbersome and require extra stepsduring surgery that make the procedure more difficult.

The aim of the present invention is to provide a satisfactory method ofpreventing wear debris from reaching the prosthesis/bone interface andbiological tissue that addresses the problems encountered with knownmethods.

According to a first embodiment the present invention provides acomponent of a prosthetic joint comprising a portion to secure thecomponent to a bone, a bearing portion having a bearing surface whereinone or more reservoirs are situated behind the bearing surface, one ormore magnet assemblies are associated with the or each reservoir and oneor more passages are provided extending between a surface of thecomponent and the or each reservoir, said component being adapted foruse with a further joint component which has a bearing surface thatincludes magnetic material or a material that in use has a magneticsurface.

According to an alternative first embodiment the present inventionprovides a component of a prosthetic joint comprising a portion tosecure the component to a bone, a bearing portion having a bearingsurface wherein one or more reservoirs are situated behind the bearingsurface, one or more magnet assemblies are associated with the or eachreservoir and one or more passages are provided extending between asurface of the component and the or each reservoir, wherein the bearingsurface includes magnetic material or a material that in use has amagnetic surface.

The bearing surface may completely, or substantially completely, bemagnetic material or material that in use has a magnetic surface.Alternatively, the bearing surface may only partially be magneticmaterial or material that in use has a magnetic surface.

The portion to secure the component to a bone is preferably a backingportion, more preferably a metal backing portion. Most preferably thebacking portion is made from non-magnetic metals and alloys such astitanium, titanium alloys (e.g. ASTM F1472-99, F1108-97a, F1295-97a,F1713-96), tantalum, CoCrMo (e.g. ASTM F75-98, F799-99 or F1537-00) andcobalt-nickel-chromium-molybdenum (CoNiCrMo; e.g. ASTM F1058-97,F562-00, F563-95, F961-96). Alternatively, the portion to secure thecomponent to a bone may be integrated in the bearing portion.

The backing portion may suitably be modified on the outer surface by,for example, roughening or coating to enhance its immediate orsubsequent fixation to bone. Examples of suitable coatings includeroughened or porous CoCrMo, titanium, titanium alloy, tantalum,hydroxyapatite and combinations thereof. These coatings may be appliedby suitable methods known in the art, such as thermal spraying orsintering. Such external coatings may also function to enclose the oreach magnetic assembly within the joint component to preventdislodgement, in particular during insertion or use.

The bearing portion may be part of a composite front section, which maysuitably be mass-produced in a factory. The composite front sectionsuitably comprises a non-magnetic shell that contains the or eachreservoir and the or each magnet assembly associated with the or eachreservoir, and the bearing portion having a bearing surface, with thebearing portion being located on the inner surface of the shell.Preferably the composite front section further comprises an additionallayer, preferably a non-magnetic layer, for example, a polymer layersuch as an ultra high molecular weight polyethylene (UHMWPE) layer, onthe outer surface of the shell. The composite front section can besecurely attached, for example by being impacted, to the backing portionusing standard methods to produce the component.

Alternatively, the bearing portion may be an individual section that canbe attached directly to the portion to secure the component to a bone.The outer surface of the bearing portion may be coated with anappropriate material that encloses the or each magnet assembly withinthe component to prevent dislodgement of the or each magnet assemblyduring insertion or use. Further, the coating improves the ability ofthe bearing portion to be attached to the portion to secure thecomponent to bone.

The bearing portion may also be an individual section that integratesthe portion to secure the component to a bone. The outer surface of saidbearing portion may be coated with an appropriate material that enclosesthe or each magnet assembly within the component to prevent dislodgementof the or each magnet assembly during insertion or use. This coating mayalso form part or all of the portion to secure the component to thebone.

The bearing portion may be constructed wholly or partially from amagnetic material. More preferably the bearing surface of the bearingportion is wholly or partially coated with a magnetic material. In onearrangement the magnetic material coats only the part of the bearingsurface that generates the majority of the debris.

The magnetic material may be made from magnetically hard or semi-hardmaterial but is preferably made from magnetically soft material with lowcoercivity such that it does not become permanently magnetised by theeffects of bearing friction or strong external magnetic fields, such asused in Magnetic Resonance Imaging (MRI) processes. Preferably thematerials have a coercivity of less than 12 Oersteds, more preferablyless than 6 Oersteds and most preferably as close to zero as possible.The material ideally has high saturation magnetic flux density (at least0.3 Tesla, preferably greater than 1.0 Tesla and more preferably greaterthan 2.0 Tesla) and high relative permeability (at least 50, preferablygreater than 100 and more preferably greater than 1000) such that weardebris created in use around the joint component is pulled towards theor each magnet assembly.

Suitable magnetic materials include metal alloys, metal oxides,intermetallic compounds, ceramics, amorphous metal alloys andcombinations thereof including metal matrix composites.

Metal alloys suitable for use include:

1. Cobalt based alloys;

2. Nickel based alloys; and

3. Iron based alloys including magnetic steels.

In general, alloys that satisfy the following conditions (in addition topossessing optimal wear and corrosion resistance for long-term implantbearing use) in terms of % weight are preferred.

60≦(Co+Fe+Ni)≦95

0≦(Mo+Cr)≦35

0≦Co≦90, preferably from 50 to 70

0≦Fe≦90, preferably from 0 to 20

0≦Ni≦90, preferably from 0 to 40

0≦Cr≦30, preferably from 5 to 15

0≦Mo≦20, preferably from 2 to 10

0≦C≦10, preferably from 0 to 6;

with any balance being made up from: Mn, Ti, Ta, Si, Al, S, P, N, V, B,Nb, Cu, Hf, Zr, W, preferably at a level of ≦15.

For example

-   -   Co 62, Ni 13, Cr 12, Mo 4, Fe 9, C<0.2    -   Co 68, Cr 14, Ni 9, Fe 5, Mo 4, C<0.2    -   Co 85, Cr 15    -   Fe 82, Cr 17, C 1    -   Fe 67, Cr 29, Mo 4    -   Fe 67, Cr 22, Ni 6, Mo 3.    -   Ni 51, Fe 48, Mn 0.5, Si 0.35

Suitable ceramics include oxides and nitrides of nickel, iron, cobaltand manganese.

e.g.

-   -   CrO₂    -   Fe₃O₄    -   CoFe₃O₄    -   NiO    -   Fe_((2 to 4))N

Ceramic materials having magnetic properties may be preferable to alloysfor use as the magnetic material. The particulate wear debris from manyceramics is highly corrosion resistant and may retain its magneticproperties in the long term. This is in contrast to metal alloys, wherethe bearing surface and particulate wear debris produced may experiencea leeching out of the more soluble ions with time (e.g. cobalt ions withCoCrMo alloys). This potentially can be detrimental to the magneticproperties of the bearing surface and particulate wear debris.

Amorphous metal alloys suitable for use in the present invention mayhave compositions similar to the metal alloys above but with highsilicon and/or boron content (e.g. Co 82, Si 8.6, Fe 4.45, B 3.15, Ni1.63).

The coating of magnetic material on the bearing surface may be formed byapplying a layer of magnetic material to the bearing surface usingcoating techniques. Alternatively, a coating can be produced by treatingthe bearing surface so as to chemically alter the material at thesurface and thus cause the formation of a layer of magnetic material.Any known coating techniques and treatment methods for producing acoating may be used. Without limitation, suitable methods for achievinga magnetic coating on the bearing surface may include welding, diffusionbonding, thermal spraying, ion implantation, plasma vapour deposition,cathode vapour deposition, oxidation, nitriding (by any of the manymethods available), hot isostatic pressing, sintering and lasercladding.

Alternatively, the bearing portion may be wholly or partiallyconstructed from a material that in use has a magnetic surface or thebearing surface may be wholly or partially coated with a material thatin use has a magnetic surface. In one arrangement the material that inuse has a magnetic surface coats only the part of the bearing surfacethat generates the majority of the debris.

Generally, the material may be non-magnetic under normal circumstancesbut when used in the bearing portion or as a coating on the bearingsurface it becomes partially or completely magnetic, with at least theexposed surface of the material being magnetic. In particular, it ispreferred that in use at least the external surface of the material is amagnetic material having properties as described above. For example, thebearing portion may be constructed from or the bearing surface coatedwith an alloy that is generally non-magnetic but during use becomesmagnetic at at least the surface due to strain induced hardening.Alternatively, the bearing portion may be constructed from or thebearing surface coated with an alloy that is generally non-magnetic butthat in use develops thin layers of magnetic oxides at the surface dueto corrosion.

Wholly or partially coating the bearing surface, preferably with amagnetic material or alternatively with a material that in use has amagnetic surface, is preferred to forming the bearing portion from amagnetic material or a material that in use has a magnetic surface. Thisis because in coating the bearing surface a smaller amount of magneticmaterial is used, which reduces the forces exerted by high externalmagnetic fields such as with MRI scanners. Additionally, if the bearingsurface is coated with magnetic material, or if the coating is appliedonly to the part of the bearing surface that generates the majority ofthe debris (for example, the polar region of a ball and socket joint asopposed to the equatorial region), rather than the magnetic materialcomprising a substantial part of the bearing portion, the magnetic fieldfrom the or each magnet assembly used to attract particles can penetratemore efficiently the area or areas where the particulate debris isformed or passes. This allows the use of lower strength, smaller andmore cost-effective magnets and magnet assemblies. This, in turn,minimises the forces exerted on the prosthesis by external magneticfields. In addition, the effect of the or each magnetic assembly onsurrounding biological tissue is reduced, and therefore the need formagnetic shielding of the or each magnetic assembly when a biologicaleffect is undesirable is reduced.

The or each magnet assembly may comprise one or more permanent magnets.Clearly, any magnet that has sufficient power to attract particles maybe used. Examples of suitable magnets include samarium-cobalt (SmCo) orneodymium-iron-boron (NdFeB) magnets. The magnets may be coated, forexample, with a corrosion resistant material such as a corrosionresistant polymer or a corrosion resistant metal such as chromium ornickel. The aforementioned types of magnet have high coercivity and highmaximum energy products (BHmax) and in addition are resistant toradiation, shock and time related demagnetisation.

The magnetic field produced by the or each permanent magnet assembly ispreferably externally shielded. This allows the effect of the field onsurrounding biological tissue to be minimised. Further, such shieldingalso reduces the impact of external magnetic fields (for example MRIscanners) on the magnet itself, and can therefore help preventdemagnetisation. Such shielding can suitably be achieved by methodsknown in the art such as the use of one or more magnetic materialssituated at suitable intervals around the magnet. The shielding materialand the or each magnet assembly may be coated together as one or moreunits with a corrosion resistant material as described above. Themagnetic permeability of the magnetic material on the bearing surfacemay also be chosen such that this material acts as a shield, or a layerof a suitable shielding material may be comprised within the component.

The material of the backing portion may alternatively, or additionally,be chosen such that the backing portion acts as a shield. For example,the backing portion may contain one or more magnetic shielding layersexternally or, preferably, internally.

The extent of shielding can be limited or removed to allow applicationof a magnetic field of an appropriate strength to the surroundingbiological tissue, giving rise to an appropriate therapeutic effect. Forexample, bone growth around the prosthesis may be enhanced by theapplication of a therapeutic magnetic field. This could enhance thesubsequent fixation of the prosthesis to bone and minimise thepossibility of dislodgement or loosening.

The entrances to the passages extending from a surface of the componentsto the or each reservoir may be located at any point on the surface ofthe components. Preferably the entrances to the passages are located ona surface which in use is not adjacent to biological tissue. In apreferred embodiment the entrances to the passages are located on ornear the bearing surface. In particular, they may be arranged around thecircumference of the bearing surface of the component, or they may belocated on a part of the bearing surface distinct from thecircumference. When the entrances to the passages are arranged aroundthe circumference of the bearing surface of the component, they may bearranged around the entire circumference or may be arranged around onlypart of the circumference, for example around a quarter or half sectionof the circumference. In one arrangement, the entrances to the passagesare located only on the area of the bearing surface that, in use, is notload bearing. Preferably there are several passages extending from asurface of the components to the or each reservoir, for example 4 ormore, preferably 10 or more, more preferably 20 or more.

Clearly the passages and reservoirs should be of sufficient size so asto be able to contain particles of the magnetic material. The totalcapacity of all of the passages and reservoirs should be sufficient tocontain the maximum total volume of wear debris particles that could beexpected to be produced during the life of the patient. It is preferredthat the total capacity of all the passages and reservoirs issignificantly greater than the volume of particles that could beexpected to be produced during the life of the patient, so that thepassages and reservoirs are unlikely to become clogged with material.For this reason it is also preferred that the size of the entrance toeach passage on the surface of the socket is at least several times thesize of the largest particles of magnetic material. The particles ofmagnetic material may be as small as 5 to 10 nm. Depending on the natureof the magnetic material, larger particles of up to 10 μm may beproduced and occasionally very large particles of up to 500 μm may beproduced. It is clearly desirable that the passages and reservoirs donot compromise the bearing surface or compromise structural support forthe bearing surface. Accordingly, the passages may, for example, haveapproximately circular entrances of from 0.5 to 5 mm in diameter. Thedepth of the passages may be, for example, from 0.5 to 5 mm.

It is further preferred that the passages are designed such that oncethe particles have entered the passage they are unlikely to exit itunder normal circumstances. For example, each passage may have anentrance portion and an end portion, with the entrance portion beingwider than the end portion.

According to a second embodiment the present invention provides aprosthetic joint suitable for replacing an existing joint comprising twocomponents dimensionally adapted to articulate with each other whereinone or both components are provided in accordance with one of the firstembodiments of the invention as described above and wherein one or bothjoint components have a bearing surface including a magnetic material ora material that in use has a magnetic surface.

Preferably, only one component of the joint is provided in accordancewith one of the first embodiments described above. The other componentof the joint may be made from any suitable material such as a ceramic orCoCrMo alloy. One or both of the components may have a bearing surfaceincluding a magnetic material or a material that in use has a magneticsurface.

Alternatively, both components of the joint may be provided inaccordance with one of the first embodiments as described above. Thebearing surface of one or both of these components may include amagnetic material or a material that in use has a magnetic surface.

The joint component and resultant joint of the present invention arehighly advantageous, as owing to the nature of the material that formsthe bearing surface of one or both portions of the joint, the weardebris created in use is at least partially magnetic. The, or at leastpart of the, wear debris is therefore attracted by the magnet assemblyinto the reservoir. The amount of debris reaching the prosthesis/boneinterface and biological tissues is therefore reduced or eliminated,alleviating the problems associated with wear debris reaching theinterface and with metal ions reaching biological tissue. A furtheradvantage of the joint component and resultant joint of the presentinvention is that they may be implanted into a patient using standardsurgical techniques for implanting prostheses. Also, the risk of jointdislocation, subluxation or micro-separation may be reduced with thejoint of the present invention, due to the magnetic pull on onecomponent by the magnet assembly in the other component.

In a further embodiment the present invention provides a system suitablefor replacing a hip joint, which comprises a head and a socketdimensionally adapted to articulate with the head, wherein the socket isprovided in accordance with one of the first embodiments of theinvention, the head has a portion for securing the head to a bone andone or both of the bearing surface of the socket and the surface of thehead substantially comprise magnetic material or material that in usehas a magnetic surface.

Alternatively, the system may comprise a head and a socket dimensionallyadapted to articulate with the head, wherein the head is provided inaccordance with one of the first embodiments of the invention, thesocket has a portion for securing the socket to a bone and a bearingsurface, and one or both of the bearing surface of the socket and thesurface of the head substantially comprise magnetic material or amaterial that in use has a magnetic surface.

The head and socket may each be of any shape, provided that they canarticulate together to mimic the movement of the joint to be replaced.Preferably the head is substantially sphere shaped and the socket is ofa corresponding shape that can engage with the curved sphere surface. Inparticular, the socket may have a corresponding cup (hollow hemisphere)shape or may be in the shape of a part of such a hemisphere. The size ofthe head and the socket is chosen depending on their intended use.

The head and the socket may each be made entirely or in part frommagnetic material or material that in use has a magnetic surface, witheach comprising the same or different materials. Preferably both thesurface of the head and the surface of the socket that articulates withthe head partially or substantially comprise magnetic material. In oneembodiment one or both of these surfaces is entirely magnetic material.In particular the head may be coated with magnetic material and/or thesocket may be coated with magnetic material in the area that articulateswith the head. In a preferred embodiment the head and the socket areboth made substantially from non-magnetic material, but contain magneticmaterial in the area where the head articulates with the socket and thearea where the socket articulates with the head.

Magnetic materials suitable for use in the system are those describedabove in relation to the first embodiment of the invention. It ispreferred that the magnetic material is an alloy or ceramic, for examplea cobalt, nickel or iron based alloy or ceramic with suitable corrosionand wear resistance for implant bearing use.

Preferably the head and the socket do not entirely comprise magneticmaterial or material that in use has a magnetic surface. In this caseany non-magnetic materials suitable for use in implants may be used toform the remainder of each component. In particular, non-magneticmetals, alloys and ceramics, for example titanium, titanium alloys (e.g.ASTM F1472-99, F1108-97a, F1295-97a, F1713-96), tantalum, CoCrMo (e.g.ASTM F75-98, F799-99 or F1537-00) and cobalt-nickel-chromium-molybdenum(CoNiCrMo; e.g. ASTM F1058-97, F562-00, F563-95, F961-96), zirconia andalumina, may be mentioned. The head and the socket may each comprise oneor more different non-magnetic materials.

Preferably the socket comprises a backing portion and a composite frontsection, which may suitably be mass-produced in a factory. The compositefront section can be fixed (e.g. impacted) into the backing portion toproduce the socket. Alternatively, the socket may comprise a backingsection which may be used to attach the socket to bone and a bearingsection, or may be an individual bearing section which has an integratedportion for attaching the socket to bone.

Preferably the socket or the head has one magnet assembly and oneassociated reservoir. The magnet assembly and the reservoir arepreferably circumferential, for example they may extend around theopening of the cup shaped socket or around the circumference of thehead.

Preferably the head comprises a core section and one or more outerlayers. The outermost layer of the head, which forms the bearingsurface, preferably includes a magnetic material. The core sectionpreferably comprises a non-magnetic material such as titanium, titaniumalloy, CoCrMo, CoNiCrMo, stainless steel or non-magnetic ceramic.

The permanent magnet assembly in the socket or head is preferablycircumferential; for example it may be loop shaped. It is preferred thatthe magnet assembly is located inside the socket or head such that it iscoplanar with at least one point of the bearing surface of the head orthe socket. More preferably the magnet assembly is located such that itis coplanar with at least two points of the bearing surface of the heador the socket.

Preferably, the magnetic assembly provides suitable field strength andis located such that a magnetic field is produced over the entire areawhere the head and socket articulate. The magnetic field may also extendto at least some of the surrounding area as well as the area of directarticulation. Alternatively, the magnetic field may extend only over aspecific localised area of the joint system, for example the area aroundthe front edge of the socket. Clearly it is preferable that the field issuch that all particles of magnetic material that come away from thesurfaces during the life of the implant are within the magnetic field atsome point to the extent that allows them to be attracted towards themagnetic assembly and reside in the reservoirs.

Both the head and the socket comprise portions for securing to a bonethat allow the head and the socket to each be attached to appropriatebones in the body during surgery.

Although the joint replacement system has been described with referenceto the replacement of a hip joint, it will be understood that the systemmay also be used to replace other joints, such as knee joints orshoulder joints.

Further provided is the use of a joint component or prosthetic jointaccording to the present invention to reduce the amount of wear debrisreaching the prosthesis/bone interface in a prosthetic joint.

In addition there is provided the use of a joint component or prostheticjoint according to the present invention to reduce or preventosteolysis.

In addition there is provided the use of a joint component or prostheticjoint according to the present invention to reduce or prevent asepticloosening.

The above uses of the joint component or prosthetic joint of the presentinvention reduce, or eliminate, the need for revision surgery which hasa high associated morbidity rate and arises due to failure of aprosthetic joint through osteolysis or aseptic loosening.

In addition there is provided the use of a joint component or prostheticjoint according to the present invention to reduce the level ofcirculating and tissue metal ions and wear particles. The metal ions maybe, for example, chromium, nickel or cobalt. The presence of circulatingand tissue metal ions has been linked with systemic disease such aschromosomal damage and cancer.

Particular embodiments of the invention are further described withreference to the accompanying drawings, which are not intended to limitthe scope of the invention.

FIG. 1 is a diagrammatic representation of a system of the presentinvention as applied to a hip replacement;

FIG. 2 is a close up view of a system of FIG. 1 of the present inventionshowing the articulating surfaces of the head and the socket;

FIG. 3 is a diagrammatic representation showing the detailed compositionof a system according to FIG. 1 of the present invention;

FIGS. 4 a-4 g show examples of shells suitable for use in a socketcomponent of FIG. 1 of the present invention;

FIG. 5 is a diagrammatic representation showing the detailed compositionof a shell according to FIG. 4 f;

FIGS. 6 a and 6 b show examples of a backing suitable for use in asocket component of FIG. 3;

FIGS. 7 a and 7 b are diagrammatic representations showing the detailedcomposition of examples of a second system according to FIG. 1 of thepresent invention;

FIGS. 8 a and 8 b show the detailed composition of examples of a thirdsystem according to FIG. 1 of the present invention;

FIGS. 9 a and 9 b show a partial magnetic coating on a socket of thepresent invention in perspective view and in cross-section; and

FIGS. 10 a and 10 b show a partial magnetic coating on a head componentof the present invention in perspective view and in cross-section.

FIGS. 1 and 2 show an embodiment of a prosthetic joint according to theinvention. The joint comprises a socket component 1 and a head component2 that articulate together. The bearing surface 3 of the socketcomponent and the bearing surface 4 of the head component each include amagnetic material. The socket component 1 includes a circumferentialmagnet system 5 associated with a reservoir 6 that has passages 7leading to the bearing surface. The head component 2 has a securingmeans 8 that may be attached to a bone.

In use the particles of bearing surfaces 3 and 4 that come away from thesurface due to wear are attracted to the magnet 5. This attraction willcause them to move towards one of the passages 7 and then into thereservoir 6 where they will remain due to their attraction to themagnet. Accordingly, the particles are prevented from reaching thebone/prosthesis interface and thus a major cause of osteolysis (boneresorption) is removed.

FIG. 3 shows, in detail, an embodiment of the socket component of aprosthetic joint according to FIG. 1 of the invention. The socketcomponent 1 comprises a backing portion 10 and a composite front portion11. The composite front portion 11 comprises a polymer layer 12,positioned in use against the backing portion. A non-magnetic shell 13is positioned between the polymer layer 12 and the bearing surface 3. Acircumferential magnet system 5 is situated in the non-magnetic shell 13and has a shielding layer 14 to shield the magnet system from biologicaltissue. The magnet system 5 is associated with a reservoir 6 that haspassages 7 leading to the bearing surface.

FIGS. 4 a-4 g show examples of a shell 13 for use in a socket component1 according to the invention. Each shell 13 comprises a number ofpassages 7. As can be seen, the passages may vary in size, shape andnumber. In FIG. 4 a cut-outs around the edge of the shell are provided,in FIG. 4 b elongate holes are provided in the shell and in FIGS. 4 c, 4d, 4 e and 4 f small circular holes are provided. In FIG. 4 g, smallcircular holes around part of the circumference are provided.

FIG. 5 shows in detail the construction of the shell of FIG. 4 f. Theinner surface is reinforced with radial supports 16 that are situated atintervals within the reservoir 6, which is linked by passages 7 to theinner surface.

FIGS. 6 a and b show examples of a backing portion 10 for use in asocket component 1 according to the invention. FIG. 6 a shows a basicbacking portion made from metal. In FIG. 6 b the backing portion furthercomprises a layer of magnetic shielding material 17 on the innersurface, which assists in the shielding of biological tissue from themagnetic field of the magnet assembly.

FIGS. 7 a and b show, in detail, a second embodiment of the componentsof a prosthetic joint according to FIG. 1. The socket 1 is a one-piececomponent, comprising a bearing portion 18 with a bearing surface 3. Acircumferential magnet system 5 is situated in bearing portion 18 andhas a shielding layer 14 to shield the magnet system. The magnet system5 is associated with a reservoir 6 that has passages 7 leading to thebearing surface. In FIG. 7 b the bearing portion 18 further has anexternal coating 19 that provides for appropriate securing of thebearing portion 18 to bone and that encloses the magnet system 5,preventing dislodgement during insertion or use.

The head component 2 comprises a non-magnetic core 15, a bearing surface4 and a securing means 8.

FIGS. 8 a and b show, in detail, a third embodiment of the components ofa prosthetic joint according to FIG. 1. The socket 1 is a two-piececomponent, comprising a bearing portion 18 with a bearing surface 3 anda backing portion 10 that are impacted together. A circumferentialmagnet system 5 is situated in the bearing portion 18 and has ashielding layer 14 that shields the magnet system. The magnet system 5is associated with a reservoir 6 that has passages 7 leading to thebearing surface 3. In FIG. 8 b the bearing portion 18 has an externalcoating 19 that can appropriately secure bearing portion 18 to thebacking portion 10 and that encloses the magnet system 5, preventingdislodgement during insertion or use.

The head component 2 comprises a non-magnetic core 15, a bearing surface4 and a securing means 8.

FIGS. 9 a and b show a further embodiment of the invention wherein themagnetic coating forming the bearing surface 3 is applied to only a partof the bearing portion 18 of the prosthetic joint socket 1 of thepresent invention. In FIGS. 9 a and 9 b the magnetic coating is appliedonly to the polar region 18 a of the bearing portion 18 of the socket 1rather than the polar 18 a and equatorial 18 b regions.

FIGS. 10 a and b show a further embodiment of the invention wherein themagnetic coating forming the bearing surface 4 is applied to only a partof the prosthetic head component 2 of the present invention. In FIGS. 10a and 10 b the magnetic coating is applied only to the polar region 2 aof the head component rather than the polar region 2 a and theequatorial region 2 b.

1. A component of a prosthetic joint comprising: a portion to secure thecomponent to a bone; a bearing portion having a bearing surface whereinat least one reservoir is situated behind the bearing surface at leastone magnet assembly associated with the reservoir; and at least onepassage extending between a surface of the component and the reservoir,said component being adapted for use with a further joint componentwhich has a bearing surface that includes at least one of a magneticmaterial and a material that in use has a magnetic surface.
 2. Acomponent of a prosthetic joint comprising: a portion to secure thecomponent to a bone; a bearing portion having a bearing surface whereinat least one reservoir is situated behind the bearing surface, andwherein the bearing surface includes at least one of a magnetic materialand a material that in use has a magnetic surface; at least one magnetassembly associated with the reservoir; and at least one passageextending between a surface of the component and the reservoir.
 3. Acomponent according to claim 1 wherein the portion to secure thecomponent to a bone is a backing portion made from at least one of anon-magnetic metal, a non-magnetic alloy, titanium, a titanium alloy,tantalum, CoCrMo, and cobalt-nickel-chromium-molybdenum. 4-6. (canceled)7. A component according to claim 1 wherein the backing portion has atleast one of an outer surface having one of a roughened surface and acoating thereon and one of a roughened and porous coating of at leastone of CoCrMo, titanium, titanium alloy, tantalum, and hydroxyapatite.8. (canceled)
 9. A component according to claim 1 wherein the bearingportion is part of a composite front section comprising: a non-magneticshell that contains the reservoir and the magnet assembly associatedwith the reservoir; the bearing portion, wherein the bearing portion islocated on the inner surface of the shell; and an additionalnon-magnetic layer on an outer surface of the shell. 10-11. (canceled)12. A component according to claim 1 wherein the bearing portion is atleast one of an individual section attachable directly to the portion tosecure the component to a bone, an individual section integrated withthe portion to secure the component to a bone, one of wholly andpartially constructed from a magnetic material, and one of wholly andpartially coated with a magnetic material.
 13. (canceled)
 14. Acomponent according to claim 12 wherein an outer surface of the bearingportion is coated with a material that encloses the magnet assemblywithin the component to prevent dislodgement of the magnet assemblyduring at least one of insertion and use. 15-16. (canceled)
 17. Acomponent according to claim 12 wherein the magnetic material is atleast one of a magnetically soft material with low coercivity and amagnetic material having a high saturation magnetic flux density andhigh relative permeability such that wear debris created in use aroundthe joint component is pulled towards the magnet assembly. 18.(canceled)
 19. A component according to claim 12 wherein the magneticmaterial is selected from a group consisting of metal matrix composites,metal alloys, a metal alloy selected from cobalt based alloys, nickelbased alloys, magnetic steels, and iron based alloys, metal oxides, ametal oxide selected from oxides of nickel, iron, cobalt, and manganese,intermetallic compounds, ceramics, a ceramic selected from oxides andnitrides of nickel, iron, cobalt, and manganese, amorphous metal alloys,an amorphous metal alloy selected from cobalt, nickel, and iron basedamorphous alloys with at least one of a high silicon and a high boroncontent, and combinations thereof.
 20. (canceled)
 21. A componentaccording claim 1 wherein the bearing portion is at least one of atleast partially constructed from and at least partially coated with atleast one of a material that in use has a magnetic surface, an alloythat is generally non-magnetic but during use becomes magnetic at atleast a surface due to strain induced hardening, and an alloy that isgenerally non-magnetic but that in use develops thin layers of magneticoxides at a surface due to corrosion. 22-23. (canceled)
 24. A componentaccording to claim 1 wherein the magnet assembly comprises at least onepermanent magnet.
 25. A component according to claim 24 wherein thepermanent magnet includes at least one of samarium-cobalt (SmCo) andneodymium-iron-boron (NdFeB).
 26. A component according to claim 1wherein a magnetic field produced by magnet assembly is externallyshielded.
 27. A component according to claim 1 wherein the passage hasan entrance located on a surface which in use is not adjacent tobiological tissue and located on or near the bearing surface. 28-29.(canceled)
 30. A component according to claim 1 wherein the passage hasan approximately circular entrance of from about 0.5 to 5 mm in diameterand has a depth of from about 0.5 to 5 mm.
 31. A prosthetic jointsuitable for replacing an existing joint comprising two componentsdimensionally adapted to articulate with each other wherein at least oneof the components has a bearing surface including at least one of amagnetic material and a material that in use has a magnetic surface, andwherein at least one of the components comprises: a portion to secure toa bone; a bearing portion having a bearing surface wherein at least onereservoir is situated behind the bearing surface; at least one magnetassembly associated with the reservoir; and at least one passageextending between a surface of the component and the reservoir. 32.(canceled)
 33. A prosthetic joint according to claim 31 wherein one ofthe components of the joint is made from one of ceramic and a CoCrMoalloy. 34-35. (canceled)
 36. A system suitable for replacing a hipjoint, which comprises a head and a socket dimensionally adapted toarticulate with the head, wherein the head has a bearing surface and aportion for securing the head to a bone, the socket has a bearingsurface and a portion for securing the socket to a bone, and at leastone of the bearing surface of the socket and the bearing surface of thehead substantially comprises one of a magnetic material and a materialthat in use has a magnetic surface, and wherein at least one of thesocket and the head comprises: at least one reservoir situated behindthe bearing surface; at least one magnet assembly associated with thereservoir; and at least one passage extending between a surface of thecomponent and the reservoir.
 37. (canceled)
 38. A system according toclaim 36 wherein the head is substantially sphere shaped and the socketis of a corresponding cup shape.
 39. A system according to claim 36wherein the head and the socket are each made at least partially fromone of a magnetic material and a material that in use has a magneticsurface, wherein each of the head and the socket may comprise at leastone of the same and different materials.
 40. A system according to claim39 wherein a surface of the head and a surface of the socket thatarticulates with the head both substantially comprise a magneticmaterial.
 41. A system according to claim 40 wherein the head and thesocket are both made substantially from non-magnetic material, butcontain magnetic material in an area where the head articulates with thesocket and an area where the socket articulates with the head.
 42. Asystem according to claim 41 wherein the non-magnetic material for eachof the head and the socket is at least one material selected fromnon-magnetic metals, alloys and ceramics, titanium, titanium alloys,tantalum, CoCrMo, cobalt-nickel-chromium-molybdenum, zirconia, andalumina.
 43. A system according to claim 36 wherein the socket comprisesat least one of a backing portion and a composite Front section, abearing section and a backing section for attaching the socket to bone,and an individual bearing section which has an integrated portion forattaching the socket to bone.
 44. A system according to claim 36 whereinat least one of the socket and the head has one magnet assembly and oneassociated reservoir.
 45. A system according to claim 44 wherein themagnet assembly and the reservoir are circumferential.
 46. A systemaccording to claim 36 wherein the head comprises a core section and atleast one outer layer.
 47. A system according to claim 46 wherein anoutermost layer of the at least one outer layer of the head forms thebearing surface and includes a magnetic material, and the core sectioncomprises a non-magnetic material comprising at least one of titanium,titanium alloy, CoCrMo, CoNiCrMo, stainless steel, and a non-magneticceramic.
 48. A system according to claim 36 wherein the magnet assemblyis located inside one of the socket and the head such that it iscoplanar with at least one point of the bearing surface of one of thehead and the socket.
 49. A system according to claim 48 wherein themagnet assembly is located such that it is coplanar with at least twopoints of the bearing surface of one of the head and the socket.
 50. Asystem according to claim 36 wherein the magnetic assembly providessuitable field strength and is located such that a magnetic field isproduced over the entire area where the head and socket articulate. 51.Use of a prosthetic joint according to claim 31 to reduce the amount ofwear debris reaching a prosthesis/bone interface in the prostheticjoint.
 52. Use of a prosthetic joint according to claim 31 to reduce orprevent osteolysis.
 53. Use of a prosthetic joint according to claim 31to reduce or prevent aseptic loosening.
 54. Use of a prosthetic jointaccording to claim 31 to reduce a level of circulating and tissue metalions and wear particles after joint replacement.
 55. A componentaccording to claim 2 wherein the portion to secure the component to abone is a backing portion made from at least one of a non-magneticmetal, a non-magnetic alloy, titanium, a titanium alloy, tantalum,CoCrMo, and cobalt-nickel-chromium-molybdenum.
 56. A component accordingto claim 2 wherein the backing portion has at least one of an outersurface having one of a roughened surface and a coating thereon and oneof a roughened and porous coating of at least one of CoCrMo, titanium,titanium alloy, tantalum, and hydroxyapatite.
 57. A component accordingto claim 2 wherein the bearing portion is part of a composite frontsection comprising: a non-magnetic shell that contains the reservoir andthe magnet assembly associated with the reservoir; the bearing portion,wherein the bearing portion is located on the inner surface of theshell; and an additional non-magnetic layer on an outer surface of theshell.
 58. A component according to claim 2 wherein the bearing portionis at least one of an individual section attachable directly to theportion to secure the component to a bone, an individual sectionintegrated with the portion to secure the component to a bone, one ofwholly and partially constructed from a magnetic material, and one ofwholly and partially coated with a magnetic material.
 59. A componentaccording to claim 58 wherein an outer surface of the bearing portion iscoated with a material that encloses the magnet assembly within thecomponent to prevent dislodgement of the magnet assembly during at leastone of insertion and use.
 60. A component according to claim 58 whereinthe magnetic material is at least one of a magnetically soft materialwith low coercivity and a magnetic material having a high saturationmagnetic flux density and high relative permeability such that weardebris created in use around the joint component is pulled towards themagnet assembly.
 61. A component according to claim 58 wherein themagnetic material is selected from a group consisting of metal matrixcomposites, metal alloys, a metal alloy selected from cobalt basedalloys, nickel based alloys, magnetic steels, and iron based alloys,metal oxides, a metal oxide selected from oxides of nickel, iron,cobalt, and manganese, intermetallic compounds, ceramics, a ceramicselected from oxides and nitrides of nickel, iron, cobalt, andmanganese, amorphous metal alloys, an amorphous metal alloy selectedfrom cobalt, nickel, and iron based amorphous alloys with at least oneof a high silicon and a high boron content, and combinations thereof.62. A component according to claim 2 wherein the bearing portion is atleast one of at least partially constructed from and at least partiallycoated with at least one of a material that in use has a magneticsurface, an alloy that is generally non-magnetic but during use becomesmagnetic at at least a surface due to strain induced hardening, and analloy that is generally non-magnetic but that in use develops thinlayers of magnetic oxides at a surface due to corrosion.
 63. A componentaccording to claim 2 wherein the magnet assembly comprises at least onepermanent magnet.
 64. A component according to claim 63 wherein thepermanent magnet includes at least one of samarium-cobalt (SmCo) andneodymium-iron-boron (NdFeB).
 65. A component according to claim 2wherein a magnetic field produced by the magnet assembly is externallyshielded.
 66. A component according to claim 2 wherein the passage hasan entrance located on a surface which in use is not adjacent tobiological tissue and located on or near the bearing surface.
 67. Acomponent according to claim 2 wherein the passage has an approximatelycircular entrance of from about 0.5 to 5 mm in diameter and has a depthof from about 0.5 to 5 mm.